Question:

In a certain medical test designed to measure carbohydrate tolerance, an adult drinks 7oz. of a 30% glucose solution. When the test is administered to a child, the glucose concentration must be decreased to 20%. How much 30% glucose solution and how much water should be used to prepare 7 ounces of a 20% glucose solution?

Book gives answer of: 14/3oz 30% glucose, 7/3oz water

Nearest I can figure is .3 + x = 7(.2), which gives x = 14/3

I doubt that's how it works, and if someone can expand on this and help me out, it would be nice.

Thanks.